1. Field of the Invention
The present invention relates to voltage regulating systems, and more particularly, to voltage regulating systems that are responsive to feed-forward information indicative of deterministic changes in the load current.
2. Description of the Related Art
A voltage regulator is a circuit that provides a substantially constant output voltage to a load from an input voltage source. Switching voltage regulators and linear voltage regulators are two types of voltage regulators. In linear voltage regulators, a pass element (e.g., a transistor) is coupled in series between the input voltage source and the load. The linear voltage regulator controls the current through and/or voltage across the pass element to maintain a constant output voltage. Another possible feature of such a regulator may be to regulate the output current in addition to the output voltage.
In a switching voltage regulator, a switch (e.g., a transistor) is coupled in series between the input voltage source and the load. The voltage regulator turns the switch on and off to regulate the output current or voltage or both and to maintain a constant output voltage. Voltage regulators are designed to operate under conditions of changing load current to maintain the output voltage within a specified tolerance range. A common design goal for a voltage regulator is to minimize the difference between the actual output voltage and a desired output voltage. The difference between the actual and the desired output voltage is referred to as the regulation error.
Feedback techniques are the most common methods for reducing the regulation error. In a voltage regulator with feedback, a signal from the output is fed back into the regulator and used to control the current or voltage or both that is provided to the load. Because feedback control is reactive, the output voltage or output current must first experience a deviation, before the regulator can respond to correct it. However, when significant changes in the load current occur, the deviation in the output voltage can be large enough to exceed acceptable operating voltage limits, before the regulator responds and causes the output voltage to recover.
One possible solution involves increasing the bandwidth of the voltage regulator control system so that it reacts more quickly to the regulation error. The downside of this solution for switching voltage regulators can be a loss of regulator efficiency, increased power dissipation, loss of noise margin, and less than optimal transient response.
Another possible solution involves using a multi-phase voltage regulator. The downside of multi-phase switching voltage regulators is that they can increase the cost and the electrical component count. Another solution is to use linear regulators. However, linear regulators are less efficient than switching voltage regulators and cause increased power dissipation. These problems occur because a linear regulator operates the pass element in its linear region, and causes the pass element to be on all the time.
Yet another solution involves incorporating phase lead feedback compensation for improving the responsiveness of the regulator. However, this method can cause a switching regulator to over-respond to a change in load current and to lose regulator stability.
It would therefore be desirable to provide voltage regulators that can maintain a regulated output voltage within a tight tolerance range, while being able to respond to significant changes in the load current.